It is known to provide a surgical tool guide having a resection guide, which assists a surgeon in making accurate and repeatable cuts during surgery. The accuracy of a cut made using a resection guide is mainly determined by the successful positioning and fastening of the guide in the operative area. Typically, a stylus is attached to the guide, which references from a reference point or marker on the body, for example, a bone. The stylus is either free to translate and/or rotate relative to the guide, so that it may be adjusted, or is rigidly fixed to the guide. An attachment mechanism mounts the stylus to the guide, and a locking mechanism locks the stylus in a desired position relative to the attachment mechanism and hence the guide. Once in the operating position, the guide can be attached to, for example, a bone using pins and/or bone screws.
It is also known to use a stylus to position a guide in joint replacement surgery. For example, during a total or partial knee replacement operation, it is necessary to resect the proximal tibia to a specific level. Existing tibial styli reference from the tibial plateau. This area of the joint is subject to considerable wear and, in a knee requiring joint replacement is likely to be damaged. Therefore, the tibial plateau does not provide a reliable reference position.
Once a stylus has been used to position a guide, it is usually removed, in order to increase the working space available to the surgeon. A problem of existing arrangements is that the removal of the stylus can cause unintentional and unnoticed movement of the cutting guide. This leads to inaccurate positioning of the cutting guide, with the result that the surgeons' incisions are misdirected.
GB 2426198 discloses a stylus assembly which has a stylus that references from the posterior femoral condyle which provides a relatively unworn reference surface. The stylus assembly is easily removed from a guide in order to prevent unwanted movement of the guide.
Whilst the stylus used in the assembly of GB 2426198 provides a reference point for performing a repeatable resection of the tibial plateau, it does not provide any feedback regarding the condition of the joint surfaces and that of the ligaments in the knee. The present invention seeks to address this issue.